U.S. Pat. No. 5,322,866 discloses a process for the production of biodegradable starch-based products, where untreated starch is mixed with biodegradable copolymers, such as polyvinyl alcohol or ethylene-vinyl alcohol, and with a plasticizer, and also with a moistening agent. Glycerol is a suitable plasticizer. Other suitable additives are talc or stearates, such as calcium stearate or zinc stearate. The biodegradable polymer blends according to U.S. Pat. No. 5,322,866 are produced via coextrusion of the molten components.
U.S. Pat. No. 6,096,809 discloses biodegradable polymer mixtures comprising at least one starch biopolymer, one plasticizer, and one polymer selected from aromatic polyesters, polyester copolymers having not only aliphatic but also aromatic blocks, polyesteramides, polyglycol, polyesterurethanes, and mixtures thereof. According to U.S. Pat. No. 6,096,809, the mixture can comprise plasticizers, stabilizers, antiflaming agents and, if appropriate, further biodegradable polymers, alongside the abovementioned polymers. According to said document it is possible to add crosslinking compounds, such as alkylketene dimers, in order to reduce the level of properties of the hydrophilic polymer.
U.S. Pat. No. 5,346,936 discloses a biodegradable single-phase starch/polymer mixture comprising chemically modified starch, emulsifying agent, plasticizer or destructuring compounds, and at least one linear polymer. The plasticizers that can be used are organic compounds which have at least one hydroxyl group, examples being glycerol, sorbitol, mannitol, D-glucose, ethylene glycol, polyethylene glycol, propylene glycol, and mixtures thereof. Suitable emulsifying agents are metal stearates, glycerol monostearates, polyoxyethylene sorbitan monolaurates, polyoxyethylene monopalmitates, polyoxyethylene stearates, and mixtures thereof. Other suitable additives are optical brighteners, stabilizers, antioxidants, flameproofing agents, dyes, fillers, and additives which increase processability during the production process.
U.S. Pat. No. 5,374,304 discloses biodegradable, clear, transparent, and flexible plastics based on amylose, which also comprise a plasticizer. Compounds suitable as plasticizer are glycerol, diethylene glycol, triethylene glycol, sorbitol, polyvinyl alcohol, citric acid adducts, and mixtures thereof.
EP 1 263 859 A1 discloses foils and coatings which comprise a mixture composed of a polymer selected from aliphatic polyesters, such as polylactic acid or polycaprolactone, starch, and beeswax or montan ester wax. The mixture according to EP 1 263 859 A1 can moreover comprise additives selected from fatty acid amides, talc, neutralizing agents, stabilizers, or dyes.
R. F. Storey et al., Polymer 35 (4), 830 to 838, 1994, and P. Bruin et al., Makromolekulare Chemie 9, 589-594, 1998, disclose degradable polyurethanes based on D,L-lactic acid, glucose, ε-caprolactone, and trimethylene carbonate homopolyesters, crosslinked by toluene 2,6-diisocyanate (TDI).
Polymer blends comprising starch have undesired high water absorption capability, which makes it more difficult to use them to produce foils, for example for the packaging sector. The mechanical properties of polymer mixtures comprising starch are moreover unsatisfactory. Addition of, for example, polyesters to these mixtures with the aim of increasing mechanical stability has an adverse effect on the costs of a corresponding biodegradable polymer mixture. The use of diisocyanates for the crosslinking of starch-polymer blends leads to products which have increased toxicity by virtue of the presence of diisocyanates, and these cannot therefore be used in the food-and-drink sector. The crosslinking brought about by diisocyanates is moreover difficult to reverse, and the biodegradability of these products is therefore inadequate.